The present invention relates to a downhole data transmission or telemetry system and method for communicating information axially along a drill string. More particularly, the present invention relates to a downhole short hop telemetry system and method, to be used with a measurement-while-drilling (MWD) system, for communicating information unidirectionally or bidirectionally between a sensor located near a drilling bit and the system axially along or through the components of the drill string.
Directional drilling involves controlling the direction of a borehole as it is being drilled. Since boreholes are drilled in three dimensional space, the direction of a borehole includes both its inclination relative to vertical as well as its azimuth. Usually the goal of directional drilling is to reach a target subterranean destination with the drill string, typically a potential hydrocarbon producing formation.
In order to optimize the drilling operation, it is often desirable to be provided with information concerning the environmental conditions of the surrounding formation being drilled and information concerning the operational and directional parameters of the downhole motor drilling assembly including the drilling bit. For instance, it is often necessary to adjust the direction of the borehole frequently while directional drilling, either to accommodate a planned change in direction or to compensate for unintended and unwanted deflection of the borehole. In addition, it is desirable that the information concerning the environmental, directional and operational parameters of the drilling operation be provided to the operator on a real time basis. The ability to obtain real time data measurements while drilling permits a relatively more economical and more efficient drilling operation.
For example, the performance of the downhole motor drilling assembly, and in particular the downhole motor, and the life of the downhole motor may be optimized by the real time transmission of the temperature of the downhole motor bearings or the rotations per minute of the drive shaft of the motor. Similarly, the drilling operation itself may be optimized by the real time transmission of environmental or borehole conditions such as the measurement of natural gamma rays, borehole inclination, borehole pressure, resistivity of the formation and weight on bit. Real time transmission of this information permits real time adjustments in the operating parameters of the downhole motor drilling assembly and real time adjustments to the drilling operation itself.
Accordingly, various measurement-while-drilling (MWD) systems have been developed that permit downhole sensors to measure real time drilling parameters and to transmit the resulting information or data to the surface substantially instantaneously with the measurements. For instance, MWD mud pulse telemetry systems transmit signals from an associated downhole sensor to the surface through the drilling mud in the drill string. More particularly, pressure or acoustic pulses, modulated with the sensed information from the downhole sensor, are applied to the mud column and are received and demodulated at the surface. The downhole sensor may include various sensors such as gamma ray, resistivity, porosity or temperature sensors for measuring formation characteristics or other downhole parameters. In addition, the downhole sensor may include one or more magnetometers, accelerometers or other sensors for measuring the direction or inclination of the borehole, weight-on-bit or other drilling parameters.
Typically, MWD systems, such as the MWD mud pulse telemetry system, are located above the downhole motor drilling assembly. For instance, when used with a downhole motor, the MWD mud pulse telemetry system is typically located above the motor so that it is spaced a substantial distance from the drilling bit in order to protect or shield the electronic components of the MWD system from the effects of any vibration or centrifugal forces emanating from the drilling bit. Further, the downhole sensors associated with the MWD system are typically placed in a non-magnetic environment by utilizing monel collars in the drill string below the MWD system.
Thus, the MWD system may be located a significant distance from the drilling bit. As a result, the environmental information measured by the MWD system may not necessary correlate with the actual conditions surrounding the drilling bit. Rather, the MWD system is responding to conditions which are substantially spaced from the drilling bit. For instance, a conventional MWD system may have a depth lag of up to or greater than 60 feet. As a result of this information delay, it is possible to drill completely through a potential hydrocarbon producing formation before detecting its presence, requiring costly corrective procedures.
In response to this undesirable information delay or depth lag, various near bit sensor systems or packages have been developed which are designed to be placed adjacent or near the drilling bit. The near bit system permits the detection of the potential hydrocarbon producing formation almost immediately upon its penetration, minimizing the need for unnecessary drilling and service costs. The drilling operation, including the trajectory of the drilling bit, may then be adjusted in response to the sensed information.
However, in order to use a near bit sensor system and permit real time monitoring and adjustment of drilling parameters, a system or method must be provided for transmitting the measured data or sensed information from the downhole sensor either directly to the surface or to a further MWD system for subsequent transmission to the surface. Various attempts have been made in the prior art to transmit the information directly or indirectly to the surface. However, none of these attempts have provided a fully satisfactory solution.
Various systems have been developed for communicating or transmitting the information directly to the surface through an electrical line, wireline or cable to the surface. These hard-wire connectors provide a hard-wire connection from the drilling bit to the surface, which has a number of advantages. For instance, these connections typically permit data transmission at a relatively high rate and permit two-way or bidirectional communication. However, these systems also have several disadvantages.
First, a wireline or cable must be installed in or otherwise attached or connected to the drill string. This wireline or cable is subject to wear and tear during use of the system and thus, may be prone to damage or even destruction during normal drilling operations. For instance, the downhole motor drilling assembly may not be particularly suited to accommodate such wirelines running through the motor, with the result that the wireline sensors may not usually be located in close proximity to the drilling bit. Further, the wireline may be exposed to excessive stresses at the point of connection between the sections of drill pipe comprising the drill string. As a result, the system may be somewhat unreliable and prone to failure, which may result in costly inspection, servicing and replacement of the wireline. In addition, the presence of the wireline or cable may require a change in the usual drilling equipment and operational procedures. The downhole motor drilling assembly may need to be particularly designed to accommodate the wireline. As well, the wireline may need to be withdrawn and replaced each time a joint of pipe is added to the drill string. These disadvantages result in a relatively complex and unreliable system for transmitting the sensed information.
Systems have also been developed for the transmission of acoustic or seismic signals or waves through the drill string or surrounding formation. The acoustic or seismic signals are generated by a downhole acoustic or seismic generator. However, a relatively large amount of power is typically required downhole in order to generate a sufficient signal such that it is detectable at the surface. In order to be able to generate a sufficient signal, the necessary power may be supplied to the generator by a hard wire connection from the surface to the downhole generator. Alternately, a relatively large power source must be provided downhole.
U.S. Pat. No. 5,163,521 issued Nov. 17, 1992 to Pustanyk et. al., U. S. Pat. No. 5,410,303 issued Apr. 25, 1995 to Comeau et. al., and U.S. Pat. No. 5,602,541 issued Feb. 11, 1997 to Comeau et. al. all describe a MWD tool, a downhole motor having a bearing assembly and a drilling bit. A sensor and a transmitter are provided in a sealed cavity within the housing of the downhole motor bearing assembly, adjacent the drilling bit. A signal from the sensor is transmitted by the transmitter to a receiver in the MWD tool. The MWD tool then transmits the information to the surface. The signals are transmitted from the transmitter to the receiver by a wireless system. Specifically, the information is transmitted by frequency modulated acoustic signals indicative of the sensed information. Preferably, the transmitted signals are acoustic signals having a frequency in the range of from 500 to 2000Hz. However, alternatively, radio frequency signals of up to 3000 mega-Hz may be used.
Further systems have been developed which require the transmission of electromagnetic signals through the surrounding formation. Electromagnetic transmission of the sensed information often involves the use of a toroid positioned adjacent the drilling bit for generation of an electromagnetic wave through the formation. Specifically, a primary winding, carrying the sensed information, is wrapped around the toroid and a secondary winding is formed by the drill string. A receiver may be either connected to the ground at the surface for detecting the electromagnetic wave or may be associated with the drill string at a position uphole from the transmitter.
Generally speaking, as with acoustic and seismic signal transmission, the transmission of electromagnetic signals through the formation typically requires a relatively large amount of power, particularly where the electromagnetic signal must be detectable at the surface. Further, attenuation of the electromagnetic signals as they are transmitted through the formation is increased with an increase in the distance over which the signals must be transmitted, an increase in the data transmission rate and an increase in the electrical resistivity of the formation. The conductivity and the heterogeneity of the surrounding formation may particularly adversely affect the propagation of the electromagnetic radiation through the formation. As well, noise in the drill string, particularly from the downhole motor drilling assembly, may interfere with the detection of the electromagnetic signals.
Thus, as with acoustic and seismic signal transmission, in order to be able to generate a sufficient electromagnetic signal, the necessary power may need to be supplied to a downhole electromagnetic generator by a hard wire connection from the surface. Alternately, a relatively large power source may be provided downhole.
Finally, when utilizing a toroid for the transmission of the electromagnetic signal, the outer sheath of the drill string must protect the windings of the toroid while still providing structural integrity to the drill string. This is particularly important given the location of the toroid in the drill string since the toroid is often exposed to large mechanical stresses during the drilling operation. Further, in order to avoid short circuiting of the system or a short circuit turn of the signals through the drill string and in order to enhance the propagation of the electromagnetic radiation through the surrounding formation, an electrical discontinuity is provided in the drill string. The electrical discontinuity typically comprises an insulative gap or insulated zone provided in the drill string. The insulative gap may be provided by an insulating material comprising a substantial area of the outer sheath or surface of the drill string. For instance, the insulating material may extend for ten to thirty feet along the drill string. Thus, the need for the insulative gap to be incorporated into the drill string may interfere with the structural integrity of the drill string resulting in a weakening of the drill string at the gap. Further, the insulating material provided for the insulative gap may be readily damaged during typical drilling operations.
Various attempts have been made in the prior art to address these difficulties or disadvantages associated with electromagnetic transmission systems. However, none of these attempts have provided a fully satisfactory solution.
U.S. Pat. No. 4,496,174 issued Jan. 29, 1985 to McDonald et. al. and U.S. Pat. No. 4,725,837 issued Feb. 16, 1988 to Rubin disclose an insulated drill collar gap sub assembly for a toroidal coupled telemetry system. The sub assembly provides a dielectric material in the insulative gap, while attempting to enhance the structural integrity of the sub assembly at the gap. Although the sub assembly may enhance the structural integrity of the drill string, the system still requires the propagation of the electromagnetic radiation through the formation to the surface. Specifically, electromagnetic waves are launched from a transmitting toroid in the form of electromagnetic waves traveling through the earth. These waves eventually penetrate the earth""s surface and are picked up by an uphole receiving system. The uphole receiving system comprises a plurality of radially extending arms of electrical conductors about the drilling platform, which are laid on the ground surface and extend for three to four hundred feet away from the drill site. These receiving arms intercept the electromagnetic waves and send the corresponding signals to a receiver.
U.S. Pat. No. 4,691,203 issued Sep. 1, 1987 to Rubin et. al. is directed at a downhole telemetry apparatus for transmitting electromagnetic signals to the surface. The apparatus includes a mode transducer designed to avoid the need for a toroidal transformer. The transducer provides a total electrical discontinuity in the drill string so that a potential difference can be produced across adjacent conducting faces of the drill string. Essentially, the adjacent conducting faces of the drill string are separated from each other by a predetermined insulative gap. Insulation around the gap is selected to induce optimum earth currents when the electrical signal is applied across the faces. Once the signal crosses the insulative gap, it is conducted to the surface through an upper portion of the drill string, where it is transferred from the drill string through a wire to an input transformer for a surface receiver. Once flowing through the transformed primary, the signal is transmitted through a wire installed in the ground near the surface. The electrical signal from the wire propagates through the earth back to the downhole sensor unit and finally completes its path into the mode transducer.
U.S. Pat. No. 5,160,925 issued Nov. 3, 1992 to Dailey et. al. and PCT International Application PCT/US92/03183 published Oct. 29, 1992 as WO 92/18882 are directed at a short hop communication link for a downhole MWD system. The system comprises a sensor module, a control module, a host module and a mud pulser. The sensor module includes a transmitter for transmitting an electromagnetic signal, indicative of the information measured by the sensor, to the control module and a receiver for receiving commands from the control module. The control module includes a transceiver for transmitting command signals and receiving signals from the sensor module. Further, the control module transmits electrical signals to the host module through a hard wire connection, which similarly connects to the mud pulser.
Both the sensor and control modules include an antenna arrangement through which the electromagnetic signals are sent and received through a short hop communication link. The sensor and control antennas are transformercoupled, insulated gap antennas. More particularly, communication between the sensor and control modules is effected by electromagnetic propagation through the surrounding conductive earth. The signal is impressed across an insulated axial gap in the outer diameter of the drill string, represented by the antennas, either by transformer coupling or by direct drive across a fully insulated gap in the assembly. The electromagnetic wave from the antenna propagates through the surrounding conductive earth, accompanied by a current in the metal drill string. As the formation conductance increases and resistance decreases, the maximum frequency with acceptable attenuation will decrease. Preferably, a frequency in the range of about 100 to 10,000 Hz is used.
U.S. Pat. No. 5,359,324 issued Oct. 25, 1994 to Clark et. al. and European Patent Specification EP 0 540 425 B1 published Sep. 25, 1996 are directed at an apparatus for determining earth formation resistivity and sending the information to the surface. The apparatus utilizes a first toroidal coil antenna mounted, in an insulating medium, on a drill collar for transmitting and/or receiving modulated information signals which travel through the surrounding earth formation. A second toroidal coil antenna is also mounted, in an insulating medium, on the drill collar for transmitting and/or receiving the modulated information signals to and from the first antenna.
Therefore, there remains a need in the industry for a real time data transmission or telemetry system and method for communicating information axially along a drill string. Further, there is a need for a telemetry system and method that communicate or transmit data measurements or sensed information a relatively short distance through components of the drill string. Still further, there is a need for the downhole short hop telemetry system and method to communicate information either unidirectionally or bidirectionally axially along or through the components of the drill string. Preferably, the system and method overcome or minimize the disadvantages or difficulties associated with previously known downhole telemetry systems and methods.
The present invention relates to a data transmission or telemetry system and a method for communicating information axially along a drill string. Further, the present invention relates to a downhole short hop real time telemetry system and a method, to be used with a downhole measurement-while-drilling (MWD) system, for communicating information axially along or through the components of the drill string. Preferably, the system and method are capable of communicating the information, unidirectionally or bidirectionally, between a downhole sensor located near a drilling bit of the drill string and the MWD system. Further, the system and method preferably communicate the information from the sensor to the MWD system through a downhole motor drilling assembly comprising the drill string. Specifically, the downhole motor drilling assembly preferably provides a closed axial conducting loop for transmission of the information.
Preferably, the within invention overcomes or minimizes the disadvantages or difficulties associated with previously known downhole telemetry systems and methods. Thus, the within invention preferably provides for a relatively high data transmission rate and a relatively low power consumption as compared to known systems and methods. Further, as stated, the information is communicated along the drill string or through the components of the drill string, preferably along or through the downhole motor drilling assembly. Thus, the communication of the information is not significantly affected by the conductance or resistance of the surrounding formation, drilling mud or other drilling fluids. As well, the drill string is not required to provide an insulative gap therein.
In one aspect of the invention, the invention comprises a method for communicating information axially along a drill string. The method comprises the step of conducting an axial electrical signal embodying the information between a first axial position in the drill string and a second axial position in the drill string through an axial conducting loop formed by the drill string, which axial conducting loop extends between the first axial position and the second axial position.
The axial conducting loop may be comprised of any portion or section of the drill string along the length of the drill string. Further, the axial conducting loop may be comprised of any of the components or elements comprising the drill string. However, preferably, the drill string between the first axial position and the second axial position comprises an inner axial conductor and an outer axial conductor. Further, preferably, the axial conducting loop is comprised of the inner axial conductor and the outer axial conductor. In this instance, the inner axial conductor and the outer axial conductor are conductively connected with each other at each of the first axial position and the second axial position.
The method may further comprise the steps of: (a) conducting through a transmitter conductor a transmitter electrical signal embodying the information; and (b) inducing from the conducting of the transmitter electrical signal the conducting through the axial conducting loop of the axial electrical signal. As well, the method may further comprise the step of inducing from the conducting of the axial electrical signal the conducting through a receiver conductor of a receiver electrical signal embodying the information.
In addition, before conducting the transmitter electrical signal through the transmitter conductor, the method may comprise the following steps: (a) receiving the information; and (b) generating the transmitter electrical signal. After conducting the receiver electrical signal through the receiver conductor, the method may comprise the step of obtaining the information from the receiver electrical signal.
In the within method, the transmitter electrical signal is comprised of a varying electrical signal. The transmitter electrical signal may be a unipolar varying electrical signal or a bipolar varying electrical signal. However, a unipolar varying electrical signal is preferred. The varying transmitter electrical signal may have any carrier frequency, voltage and current capable of inducing the conducting of the axial electrical signal through the axial conducting loop. Preferably, the transmitter electrical signal is comprised of a varying electrical signal having a carrier frequency of between about 10 kilohertz and about 2 megahertz, and more preferably, about 400 kilohertz. Further, the transmitter electrical signal preferably has a voltage of between about 2 volts (peak to peak) and about 10 volts (peak to peak), and more preferably, about 5 volts (peak to peak).
In another aspect of the invention, the invention comprises a telemetry system for communicating information axially along a drill string. The system comprises:
(a) an axial conducting loop formed by the drill string for conducting an axial electrical signal embodying the information between a first axial position in the drill string and a second axial position in the drill string, which axial conducting loop extends between the first axial position and the second axial position; and
(b) a transmitter for transmitting the information to the axial conducting loop.
The axial conducting loop of the system may be comprised of any portion or section of the drill string along the length of the drill string. Further, the axial conducting loop may be comprised of any of the components or elements comprising the drill string. However, preferably, the drill string between the first axial position and the second axial position comprises an inner axial conductor and an outer axial conductor. Further, preferably, the axial conducting loop is comprised of the inner axial conductor and the outer axial conductor.
As well, in the preferred embodiment, the axial conducting loop is further comprised of a first conductive connection between the inner axial conductor and the outer axial conductor at the first axial position and is further comprised of a second conductive connection between the inner axial conductor and the outer axial conductor at the second axial position.
The system also preferably comprises a receiver for receiving the information from the axial conducting loop. In the preferred embodiment, the transmitter is located adjacent to one of the first axial position and the second axial position and the receiver is located adjacent to the other of the first axial position and the second axial position.
Any transmitter capable of transmitting the information to the axial conducting loop may be used. However, the transmitter is preferably comprised of a transmitter conductor for conducting a transmitter electrical signal embodying the information such that conducting of the axial electrical signal in the axial conducting loop will be induced from the conducting of the transmitter electrical signal in the transmitter conductor. As well, the transmitter further preferably comprises a transmitter processor for receiving the information and for generating the transmitter electrical signal.
Similarly, any receiver capable of receiving the information from the axial conducting loop may be used. However, the receiver is preferably comprised of a receiver conductor for conducting a receiver electrical signal embodying the information such that conducting of the receiver electrical signal in the receiver conductor will be induced from the conducting of the axial electrical signal in the axial conducting loop. As well, the receiver further preferably comprises a receiver processor for receiving the receiver electrical signal and for obtaining the information from the receiver electrical signal.
In addition, the transmitter is preferably a transceiver which is capable of both transmitting and receiving the information. Similarly, the receiver is preferably a transceiver which is capable of both transmitting and receiving the information. Thus, although the information may be communicated in one direction only along the drill string, in the preferred embodiment, the information is able to be communicated bidirectionally along the drill string.
In both the method and system of the within invention, the transmitter conductor may be comprised of any conductor capable of conducting the transmitter electrical signal such that conducting of the axial electrical signal in the axial conducting loop will be induced from the conducting of the transmitter electrical signal in the transmitter conductor. Preferably, the transmitter conductor is comprised of a transmitter coil comprising a plurality of windings. Further, the transmitter conductor preferably includes a magnetically permeable toroidal transmitter core and the windings of the transmitter coil are wrapped around the transmitter core. The transmitter coil may include any number of windings compatible with the functioning of the transmitter conductor as described above.
The receiver conductor may be comprised of any conductor capable of conducting the receiver electrical signal embodying the information such that conducting of the receiver electrical signal in the receiver conductor will be induced from the conducting of the axial electrical signal in the axial conducting loop. Preferably, the receiver conductor is comprised of a receiver coil comprising a plurality of windings. Further, the receiver conductor preferably includes a magnetically permeable toroidal receiver core and the windings of the receiver coil are wrapped around the receiver core. The receiver coil may include any number of windings compatible with the functioning of the receiver conductor as described above.
The inner axial conductor and the outer axial conductor may each be comprised of any of the components or elements of the drill string. However, preferably, the drill string is comprised of a downhole motor drilling assembly and the inner and outer axial conductors are each comprised of one or more components of the downhole motor drilling assembly. In the preferred embodiment, the inner axial conductor is comprised of components of a drive train for the downhole motor drilling assembly. The outer axial conductor is comprised of a housing for the downhole motor drilling assembly.
Further, in the preferred embodiment, the downhole motor drilling assembly defines an annular transmitter space between the drive train and the housing and defines an annular receiver space between the drive train and the housing. The transmitter conductor and the receiver conductor are preferably located in the annular transmitter space and the annular receiver space respectively. Further, the transmitter conductor and the receiver conductor are preferably located between the first axial position and the second axial position.